Synthesis and SAR study of N-(4-hydroxy-3-(2-hydroxynaphthalene-1-yl)phenyl)-arylsulfonamides: Heat shock protein 90 (Hsp90) inhibitors with submicromolar activity in an in vitro assay

Article abstract of DOI:10.1016/j.bmcl.2008.08.022

Heat shock protein 90 is emerging as an important target in cancer chemotherapy. In a program directed toward identifying novel chemical probes for Hsp90, we found N-(4-hydroxy-3-(2-hydroxynaphthalene-1-yl)phenyl)benzene sulfonamide as an Hsp90 inhibitor with very weak activity. In this report, we present a new and general method for the synthesis of a variety of analogs around this scaffold, and discuss their structure-activity relationships.

Full text of DOI:10.1016/j.bmcl.2008.08.022

Bioorganic & Medicinal Chemistry Letters 18 (2008) 4982–4987
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and SAR study of N-(4-hydroxy-3-(2-hydroxynaphthalene-1-yl)phenyl)-
arylsulfonamides: Heat shock protein 90 (Hsp90) inhibitors with submicromolar
activity in an in vitro assay
Thota Ganesh a,b, , Pahk Thepchatri a,b, Lian Li a, Yuhong Du a, Haian Fu a, James P. Snyder a,b, Aiming Sun a,b
*
a Chemical Biology Discovery Center, Emory University, 1510 Clifton Road, Atlanta, GA 30322, USA
b Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, GA 30322, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Heat shock protein 90 is emerging as an important target in cancer chemotherapy. In a program directed
toward identifying novel chemical probes for Hsp90, we found N-(4-hydroxy-3-(2-hydroxynaphthalene-
1-yl)phenyl)benzene sulfonamide as an Hsp90 inhibitor with very weak activity. In this report, we pres-
ent a new and general method for the synthesis of a variety of analogs around this scaffold, and discuss
their structure–activity relationships.
Received 17 June 2008
Revised 6 August 2008
Accepted 8 August 2008
Available online 14 August 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Heat shock protein 90
Sulfonamides
FP assay
Suzuki-coupling
Structure-based design
Antiproliferative activity
Molecular chaperones are a class of proteins that are responsi-
ble for the correct folding and maturation of several cellular client
proteins.1 One among those chaperones is the heat shock protein
90 (Hsp90), which recently emerged as a very important and vali-
dated target in several diseases including cancer, neurodegenera-
tion, viral, fungal, and microbial infection.2,3 Hsp90 chaperone
activity is found to be essential for the stability and function of a
number of conditionally expressed signaling proteins, as well as
for the mutated, chimeric, and/or overexpressed signaling proteins
that promote cell growth and survival.3 The client proteins found
to interact with Hsp90 include Raf-1, mutant BRaf, IGF-IR, Akt,
HER2, C-Met, C-Kit, mutant EGFR, and others.4,5 These client mem-
bers are found to play a crucial role in various types of cancers2 and
are found to undergo proteosome-mediated degradation when
Hsp90 activity is inhibited.6,7
The natural product geldanamycin (GM) and its synthetic ana-
log (17-AAG) were found to bind to the ATP binding site on the
N-terminal domain of the Hsp90 and inhibit ATP-dependent chap-
erone activities.8 Only the synthetic derivative 17-AAG is currently
being evaluated for clinical use. Though Hsp90 is expressed abun-
dantly in most tissues, studies employing GM, 17-AAG, and other
compounds have concluded that cancer cells are more sensitive
to Hsp90 inhibition compared to normal cells.9 This conclusion is
further supported by the studies of Kamal et al.,10 who demon-
strated that tumor cell Hsp90 is found to be in an activated com-
plex with co-chaperones, whereas Hsp90 in normal tissue resides
in a free and uncomplexed state. These observations gave the
impetus to develop novel and effective small molecule Hsp90
inhibitors, and further affirm the notion that Hsp90 inhibition
leads to selective killing of cancer cells over normal cells.
Structure-based design and high-throughput (HTS) screening
efforts are underway to identify novel chemical scaffolds that can
potentially generate lead structures for further development.11 So
far, this work has produced at least two clinical candidates (PU-
H71,12 CNF202413) and several other preclinical candidates from
the pyrazole/isoxazole class of compounds, demonstrating suc-
cessful Hsp90 activity in both in vitro and in vivo tumor models.14
Under the MLSCN program,15 we recently identified aminoquin-
olines by HTS16 as a novel class of Hsp90 inhibitors. The work was
complemented by ligand-based design and virtual screening exer-
cises. Within this context, structures 1 and 2 (Fig. 1) were previ-
ously identified as Hsp90 blockers by means of virtual screening
performed by Barril et al.17 The compounds were found to show
low micromolar activity in the malachite green assay18 and subse-
quently in an FP assay.19 However, these analogs showed a very
poor activity in a cell growth inhibition assay (2: IC50 = 29 lM).
Moreover, a very limited SAR study on the N-(4-hydroxy-3-(2-
hydroxynaphthalene-1-yl)phenyl)benzene sulfonamide scaffold
was reported.17 This prompted us to perform a more expanded
* Corresponding author. Tel./fax: +1 404 727 6689.
E-mail address: tganesh@emory.edu (T. Ganesh).
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.08.022

T. Ganesh et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4982–4987
4983
structure analysis suggested modifications could be performed
on site B by replacing the OH group with NH2, F, etc. In addition,
more than one functional group can be added to the middle ring,
while the sulfonamide tail can be moved to other positions on
the same ring. At site C with a limited SAR, there is a room for mod-
ification such as replacing the two chlorines with hydroxyl groups
combined with the modification at sites A and B to explore poten-
tial activity enhancement.
At this juncture, we recognized the lack of a general synthetic
strategy for preparing the contemplated compounds. Only one syn-
thetic method making use of the preformed N-arenesulfonyl-p-
benzoquinonimines as starting materials had been reported in a
Russian journal.20 Unfortunately, the procedure is unsuitable to a
wide range of quinones. Thus, we envisioned an alternative and
versatile synthetic method for N-(4-hydroxy-3-(2-hydroxynaph-
thalene-1-yl)phenyl)benzene sulfonamide. Below, we show that
this method is applicable to a variety of analogs by means of a split
pool synthetic approach as shown in Schemes 1 and 2. A prelimin-
ary SAR for these analogs is also described.
The synthesis of 1–2 and their analogs is depicted in Scheme 1.
Thus, 2-bromo-4-nitroanisole or 2-bromo-4-nitroanilines (4a or
4b) were subjected to the Suzuki–Miyaura cross-coupling reac-
tion21 with 2-ethoxynaphthalen-1-ylboronic acid in a microwave
initiator for 15 min to produce product 5 in 95–98% yield. To our
surprise, such a cross-coupling strategy does not seem to have
been reported previously for unsymmetrical 2,20-binaphthols
and/or 1,10-biphenols, though palladium-mediated procedures
have been employed to generate self-coupled symmetrical 1,10-
binaphthols or 2,20-biphenols.22 The methyl- and ethyl-ethers
were deprotected by treating 5a and 5b with borontribromide in
dichloromethane solution, then the resulting hydroxyl and amino
groups (from 5a) or two hydroxyls (from 5b) were protected with
Boc-groups before reducing the nitro group by hydrogenation with
10%–palladium on carbon. The resulting amine was subsequently
treated with substituted arylsulfonylchlorides in pyridine to pro-
vide Boc-protected sulfonamides. The latter were subjected to
2%-trifluoroacetic acid in dichloromethane to provide final prod-
ucts 1–2, 6–7.23
Site A
HO
O
OH
R
R
O
S
Site B
N
H
Site C
1
. R = H
2. R = Cl
Figure 1. Potential sites for modification and SAR study.
SAR evaluation on this scaffold and to devise a synthetic method
amenable to generating a variety of analogs. For instance, only
derivatives on the terminal phenyl ring extending from the sulfone
unit were reported; the naphthalene and middle rings remaining
untouched.
The previous crystallographic investigation of 2 by Barril et al.
reveals that its naphthalene ring is buried deep within the ATP
binding pocket in the N-terminal region of Hsp90.17 Compound 2
follows the general pharmacophore established by other known
Hsp90 inhibitors (Fig. 2): contact with the hydrophobic cluster
by the naphthalene moiety and participation in a hydrogen bond-
ing network with residues Thr184 and Asp93 (the numbering re-
fers to Hsp90a). Analysis of the available steric space, and
augmentation of the hydrophobic contacts and hydrogen bonds
were considered during the optimization of the arylsulfonamide
series.
The possible sites for modification are outlined in Figure 1. Site
A: The 2-naphthol ring could be replaced with 2-phenol, 3,4-ben-
zodioxane-2-phenol, and 2-hydroxy-carbazole. The latter was con-
sidered to be able to provide not only bulkiness to fill the cavity
observed in the X-ray model, but also scaffold hydrophilicity which
can promote increased compound solubility. Likewise, crystal
The palladium cross-coupling strategy appeared promising for
generating a variety of building blocks such as biphenol (8) and
aminophenol ether (11). Indeed both these intermediates were
synthesized analogous to 5 and were carried forward by similar
synthetic steps for 1 to provide 9a–g, 10a–c, and 12a–g. Selective
demethylation of 12a with either borontribromide or aqueous
hydrogen bromide yielded only methylenedioxy ring opened prod-
uct 13. As part of our study, we decided to prepare 17, a benzodi-
oxane moiety as a replacement for the naphthalene core of 2. To
this end, 5-hydroxybenzo-1,3-dioxo-4-yl-boronic acid (14) was
synthesized albeit in a very low yield and in a poor quality as
shown in Scheme 2. Coupling 14 with 2-bromo-4-nitrophenol by
the same Suzuki procedure provided intermediate 16 in a very
low yield. Nevertheless, this was smoothly carried through to the
final product 17 as shown in Scheme 2.
Docking calculations were performed to determine if the pro-
posed synthesized analogs (6c, 13, and 17) could attain a binding
pose similar to that of the X-ray pose of 2 (Fig. 2). Schrödinger’s
GLIDE24 program was utilized for the docking calculation and the
receptor was downloaded from the Protein Data Bank (PDB ID:
2BZ5).25 The receptor geometry was optimized using Schrödinger’s
protein preparation protocol. Receptor optimization was con-
strained to 0.3 Å for all atoms. All waters were deleted except
150 and 286. Examination of other Hsp90 crystals showed water
150 to be an important interaction for a variety of Hsp90 inhibi-
tors.8,11a,12,17 Water 286 was retained since GLIDE varied the poses
tremendously for sulfonamide compounds when it was removed,
suggesting 286 was important exclusively for the sulfonamide
Figure 2. Docking of 6c (blue), 13 (yellow), 17 (green) at N-terminal ATP binding
site of Hsp90 (black, PDB: 2bz5). Docking poses are overlapped with co-crystallized
pose of compound 2 (red). Figure shows that the docking poses were able to
reproduce most heavy-atom positions of the crystal pose. Hydrogen, water, and
residue atoms were not displayed. Coordinates for poses can be provided upon
request.

4984
T. Ganesh et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4982–4987
OH
Br
HO
O
HO
O
ii-vi
HO
B
O
B(OH 2
)
X
X
O
iii-vi
HO OH
O
X
X
X
R3
R2
S
O
3
R
S
N
O2N
i
i
H
N
H
O2N
O2N
4a: X = NH2
4b: X = O
4c: X = O
R
5a:X =
NH2
2
M
e
R
R
1
8a:X =
8c:X = OH
NH2
R
5b: X = OMe
H
R1
X = OH or NH2
O
O
1: X = OH, R, R1, R2, R3 = H
3
9a: X = OH, R, R3 = Cl, R1, R2 = H
: X= OH, R = NO2, R , R , R = H
9c: X = OH, R2 = CH3, R, R1, R3 = H
9d: X= OH, R1, R2 = OCH3, R, R3 = H
: X = OH, R, R = C
l
, R1, R2 = H
i
2
O
1
2
3
9b
6a: X = OH, R = CN, R1, R2, R3 = H
X = OH, R, R2 = OCH3, R1, R3 = H
B
6b
:
HO OH
iv
iv
2
H
6c: X = OH, R = OCH3, R = O
1
2
3
1
R , R3 = H
9e
9f
: X = OH, R = NH2, R , R , R = H
1
2
3
1
: X = OH, R = NO2, R, R , R = H
6d: X = OH, R, R2 = OH, R , R3 = H
O
O
9g: X= OH, R1 = NH2, R, R2, R3 = H
7a : X = NH2, R, R , R2, R3 = H
iii-vi
1
O
O
O
O
2
1
3
7b: X = NH2, R, R3 = Cl, R1, R2 = H
7c : X = NH2, R, R2 = OCH3, R1, R3 = H
7d: X = NH2, R, R2 = OH, R1, R3 = H
10
a
: X = NH2, R = CH3, R, R , R = H
NH2
NH2
10b: X = NH2, R1, R2 = OCH3, R, R3 = H
10c: X = NH2, R1, R2 = H, R, R3 = Cl
O
O
R3
R2
S
O2N
N
H
11
R
R1
OH
ii or vii
Cl
12a: R, R3 = Cl, R1, R2 = H
12b: R = NO2, R1, R2, R3= H
O
OH
NH2
1
3
12c
:
R2 = CH3, R, R , R = H
O
O
12d: R1, R2 = OCH3, R, R3= H
12e: R = NH2, R1, R2, R3= H
iv
S
N
H
1 = NO2, R, R2, R3 = H
:
R
12f
Cl
12g: R1 = NH2, R, R2, R3= H
iv
13
Scheme 1. Synthesis of N-(4-hydroxy-3-(2-hydroxynaphthalene-1-yl)phenyl)arylsulfonamides and analogs. Reagents and conditions: (i) 4a or 4b (1 equiv), boronic acids
(1.8–2 equiv), Pd(PPh3)4 (5–10 mol%), K2CO3 (3–3.3 equiv), DME/EtOH/H2O (3:2:1 ml), microwave initiator, 15 min, 160 °C, 95–98%; (ii) BBr3, CH2Cl2, ꢀ78 °C–rt, 1 h, 85–90%;
(iii) Boc2O, DMAP, THF, reflux, 3–4 h, 95%, (iv) H2, 10% Pd–C, MeOH/EtOAc (6:2 ml), 12 psi, 1 h, 80–85%; (v) ArSO2Cl, Py, 100%; (vi) 2% TFA in CH2Cl2, rt, 90%; (vii) aq HBr, 80 °C,
65%.
Hsp90 inhibitors. Standard docking precision was performed in
which non-planar amide bond conformations were penalized and
van der Waals radii were scaled to a factor of 0.8. No constraints
were used for the docking calculation. Each compound structure
was allowed to generate up to 5 poses. The Glide docking poses
for 2 and its analogs were energy-rescored using MMGBSA.26 The
top scoring MMGBSA pose of each analog was overlaid with the
crystallographic pose as shown in Figure 2. Although the Glide
score and the MMGBSA rescore favor different compounds as
shown in Table 1, the overall overlap shows that the different sul-
fonamide analogs take advantage of the same protein-ligand inter-
actions with the Hsp90 receptor as 2.
Based on the published X-ray crystal data of Barril et al. and our
computational docking results, we decided to retain the 3,4-diox-
ane moiety and prepare derivatives by altering other parts of the
molecule. Difficulties in the preparation of good quality boronic
acid 14 and the low yields in coupling reactions with it prompted
us to revise the synthetic strategy as shown in Scheme 2. A known
iodide building block 1527 was prepared in large quantity, starting
from sesamol, and this was coupled to various commercially avail-
able boronic acids by Suzuki-coupling to generate intermediates
18, 20, and 22 in excellent yields. All of the compounds were sub-
jected to synthetic steps similar to those used in Scheme 1 to gen-
erate final products 19, 21, and 23 as shown in Scheme 2.
(6a–6d) appear to be tolerated and thereby retain activity.
Replacing the OH on the middle ring with amine decreased the
activity (7b–d). Substituting the 2-naphthol unit with the less
bulky 2-phenol moiety completely eliminated activity (9b–g and
10a–b), except for 9a which showed about 20-fold less activity
than 2. However, replacing it with the 3,4-methylenedioxy-2-
phenol moiety was well tolerated and decreased the activity by
approximately 1.5- to 2-fold (17). This observation reinforces
the suggestion made by the docking model that substituents
equal in size or bulkier than the 2-naphthol ring might be better
in this region to fill the hydrophobic cavity. Surprisingly, how-
ever, 13 exhibits a submicromolar IC50 approximately equal to
the IC50 of 2.
The compounds presented in Table 2 were also tested in the
Western blot assay by examining client protein (HER2, Raf-1,
PRAS40) degradation. Disappointingly, none of the analogs
showed any promising effect, except 2 and 13, both of which pos-
sess IC50 values of approximately 20 lM in HER2 degradation.
However, neither had any effect on Raf-1 and PRAS40. Though,
it is difficult to hypothesize that these analogs bind to Hsp90 pro-
tein with high affinity, but do not enforce disruption of client
member association, it could be speculated to their poor perme-
ability properties which might cause them to be less potent in
cell-based WB assay. To support this hypothesis, we predicted
ADME properties for the best active compounds by QikProp soft-
ware.29 As shown in Table 3, the compounds 2, 6c, 13, and 17 are
outside of the projected range.
The best active sulfonamides (2, 6c, 6d, 13, and 17) in FP assay
were also tested in cell growth inhibition assay against HER2 over-
expressing SKBr3 breast cancer cells.30 As shown in Table 2, these
derivatives exhibited only low micromolar IC50 values in this cell
line, however, these values were only about 1.4- to 3.1-fold (except
All synthesized compounds were tested in a fluorescent polar-
ization (FP) assay,28 which measures the interaction of small mol-
ecule ligands with fluorescently labeled GM and displaces the
latter from the ATP binding site of Hsp90. To our surprise, we
have not identified compounds more active than 2. Apart from
the analogs tabulated in Table 2, the other analogs have shown
no inhibitory activity at the maximum concentration tested
(50 lM). Only structural modifications at the terminal phenyl ring

T. Ganesh et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4982–4987
4985
O
O
O
O
O
O
O
v-viii
Cl
i
ii
iii
Br
O
HO
O
O
HO
OH
O
MOMO
HO
HO
O
OH
Sesamol
B(OH)2
OH
S
N
H
14
O2N
16
O2N
Cl
iv
17
B(OH)2
B(OH)2
F
H2N
O
H2N
O
MOMO
iii
iii
I
15
O
B(OH)2
O
F
MOMO
H2N
O
O
iii
22
MOMO
H2N
H2N
O
O
18
vii-viii
MOMO
O
O
F
HO
20
H2N
vii-viii
vii-viii
O
O
R3
R2
S
R
1
N
H
O
O
O
HO
O
HO
R1
H
O
N
3
2
O
S
O
23a: R, R , R = H, R = CH
O
3
R3
R2
S
1
3
2
R
23b
: R, R , R = H, R = F
N
3
1
2
H
23c: R, R = H, R = NO , R = Cl
2
R
3
1
2
3
R1
R3
23d: R = NO , R , R , R = H
2
R1
vi
1
2
3
R2
23e
: R = NH , R , R , R = H
2
1
2
21a: R, R = Cl, R , R = H
2
3
1
23f: R, R , R = H, R = C
O
O
H
3
1
2
1
3
2
19a: R, R = Cl, R , R = H
21b
: R, R , R = H, R = CH
3
21c: R, R , R = H, R = F
21d: R, R = H, R = CN, R = F
3
1
2
23g: R, R = H, R = CN, R = F
3
1
2
19b
: R, R = H, R = CN, R = F
1
3
2
1
2
3
23h
: R = NO , R, R , R = H
1
3
2
2
19c: R, R , R = H, R = COOH
1
3
2
vi
1
2
3
23i: R = NH , R, R , R = H
2
Scheme 2. N-(4-Hydroxy-3-(5-hydroxybenzo-(1,3)-dioxol-4-yl)phenyl)benzene sulfonamides. Reagents and conditions: (i) NaH, MOMCl, DMF, 0 °C–rt, 98%; (ii) n-BuLi, THF,
B(OMe)3, ꢀ78 °C, then 10% HCl, rt tech-grade (50%); (iii) 15 (1 equiv, 2 mmol), boronic acids (1.8–2 equiv), Pd(PPh3)4 (5–10 mol%), K2CO3 (3–3.3 equiv), DME/EtOH/H2O
(3:2:1 ml), microwave initiator, 15 min, 160 °C, 90–95% (except for the 16 which only obtained in 20% yield based on recovered SM); (iv) n-BuLi, THF, I2, 0 °C–rt; (v) Boc2O,
DMAP, THF, reflux, 3–4 h, 95%; (vi) H2, 10% Pd–C, MeOH/EtOAc (6:2 ml), 12 psi, 1 h, 80–85%; (vii) ArSO2Cl, Py, 100%; (viii) 2 M HCl, THF/MeOH, 90%.
Table 1
Table 2
Docking scores for compound 2 and higher affinity compounds
Inhibitory activities of sulfonamides against FP assay and SKBr3 breast cancer cellsa,b
Compound
MMGBSA (kcal/mol)
Gscore (kcal/mol)
Compound
IC50
FP
(
l
M)
Compound
IC50
FP
(lM)
2
ꢀ44.6
ꢀ42.1
ꢀ41.3
ꢀ40.4
ꢀ8.1
ꢀ8.6
ꢀ7.1
ꢀ7.9
SKBr3
SKBr3
6c
13
17
1
2
4.5
na
6.5
na
9a
13
17
21a
21b
21c
23a
23c
23g
19.4
0.55
1.7
na
6.0
4.4
na
na
na
na
na
na
0.70
4.5
2.5
1.3
1.8
9.4
6a
6b
6c
6d
7b
7c
7d
na
14.5
9.7
>50
na
na
na
31.3
19.6
28.0
26.0
27.0
for 6d) less to IC50 values observed for a known pyrazole inhibi-
tor.31 Nonetheless, the potencies of 2, 6c, 13, and 17 are at least
2.6- to 11-fold less in antiproliferative assay compared to the
in vitro binding (FP) assay. Further studies are necessary to explain
the activity differences in the two assays, but partly could be
attributed to their poor cell permeability properties as predicted
by QikProp.
In conclusion, a ligand-based design strategy centered on the
sulfonamide scaffold was conceived to develop effective Hsp90
inhibitors. Although the anticipated nanomolar activity was not
observed by examining synthetic representatives of this scaffold,
a new and versatile synthesis was developed. The procedure
should not only enable us to prepare a number of analogs for
SAR, but also may be generally applicable for the synthesis of
25.0
9.5
na, not tested in SKBr3 cells.
a
Mean of two independent determinations.
b
The other compounds which did not show any inhibitory effect up to 50
concentration are not shown in this table.
lM
unsymmetrical biphenols and binaphthols, for example 5, 8, 11,
16, 18, 20, and 22. The SAR study suggests that still more work
needs to be done to manipulate the naphthalene moiety and also
the middle phenyl ring of the scaffold, an effort that will be exerted
in due course.

4986
T. Ganesh et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4982–4987
layer was on usual work up gave black residue, which was purified by silica gel
Table 3
Predicted cell membrane permeabilitya
chromatography by eluting with 20–30% ethyl acetate in hexanes to provide
diol, 1-(2-hydroxy-5-nitrophenyl)naph-thalen-2-ol (400 mg, 87%). 1H NMR
(400 MHz, CDCl3): d 8.23 (dd, 1H), 8.18 (d, 1H), 7.83 (d, 1H), 7.80 (dd, 1H), 7.37
(m, 2H), 7.26 (m, 1H), 7.21 (d, 1H), 7.14 (d, 1H). 13C NMR (100 MHz): d 160.3,
151.9, 141.8, 133.1, 131.9, 129.4, 128.9, 128.7, 128.0, 126.5, 124.4, 123.8, 121.7,
2
6c
13
17
Ranges (nm/s)
<25 poor,
>500 great
<25 poor,
>500 great
Caco2
242
84.9
35.1
81.8
249.7
491.9
118.1, 117.0, 112.5. HRMS Calcd for
C16H12N4O, 282.07583; observed
282.07608 (M+H). To the above diol-compound (400 mg, 1.43 mmol) in
tetrahydrofuran (10 ml) were added (Boc)2O (4.3 mmol, 3 equiv), DMAP (cat),
and Et3N (3.6 mmol, 2.5 equiv), and the reaction mixture was refluxed for 4 h.
Reaction mixture was cooled and filtered through a short silica gel column,
eluting with 10% ethyl acetate in hexanes. The filtrate was concentrated to give
the Boc-protected product (700 mg, 99%). 1H NMR (400 MHz, CDCl3): d 8.35
(dd, 1H), 8.28 (d, 1H), 7.94 (d, 1H), 7.88 (d, 1H), 7.52–7.38 (m, 5H), 1.36 (s, 9H),
1.14 (s, 9H). The above compound (650 mg, 1.35 mmol) was dissolved in
EtOAc/MeOH (6:2, 6 ml) and Pd–C was added (10% on charcoal) and
hydrogenated at 12 psi for 45 min. The catalyst was filtered off through a
short silica gel column by eluting with dichloromethane. The filtrate was
concentrated to give amino-product (490 mg, 80%), which was used for the
next reaction. 1H NMR (400 MHz, CDCl3): d 7.84 (d, 1H), 7.80 (dd, 1H), 7.61 (d,
1H), 7.39 (m, 3H), 7.06 (d, 1H), 6.72 (dd, 1H), 6.61 (d, 1H), 1.39 (s, 9H), 1.07 (s,
9H). HRMS Calcd for C26H30NO6, 452.20576; observed 452.20676 (M+H). To the
above solution of amine (40 mg, 0.088 mmol) in pyridine (1 ml) was added 2,5-
dichlorobenzenesulfonyl chloride (36 mg, 1.4 equiv) and stirred for 8 h. The
pyridine was removed and the residue was dissolved in dichloromethane
(2 ml) and TFA (0.3 ml) was added, and the reaction mixture was stirred at
room temperature for 8 h. The reaction mixture was diluted with ethyl acetate
and worked up as usual. The crude mass obtained was purified by silica gel
preparative-TLC eluting with 0.8% methanol in dichloromethane to provide 2
(35 mg, 90%). 1H NMR (400 MHz, CDCl3): d 7.91 (d, 1H), 7.82 (d, 1H), 7.78 (d,
1H), 7.42 (m, 2H), 7.34 (m, 2H), 7.21 (m, 2H), 6.98 (d, 2H), 6.95 (d, 1H). 13C NMR
(100 MHz): d 153.4, 151.7, 137.5, 134.3, 133.8, 133.0, 132.8, 131.9, 131.4,
129.7, 129.3, 128.6, 128.4, 127.7, 127.6, 127.0, 124.2, 123.7, 120.7, 118.0, 117.7,
MDCK
439.3
128.8
a
Schrodinger’s QikProp employed for these calculations.
Acknowledgments
This work was supported by the US National Institutes of Health
1 U54 HG003918-02 and 1R03MH076499-01, and encouraged by
Professor Dennis Liotta (Emory University).
References and notes
1. Whitesell, L.; Lindquist, S. L. Nat. Rev. Cancer 2005, 5, 761.
2. Solit, D. B.; Chiosis, G. Drug Discov. Today 2008, 13, 38. and reference cited their
in.
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6. Mimnaugh, E. G.; Chavany, C.; Neckers, L. J. Biol. Chem. 1996, 271, 22796.
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113.1. HRMS Calcd for C22H15Cl2NO4S, 459.00934; observed 459.009343.
Similar procedures were employed to make other compounds. 1H NMR data
(recorded on Unity-400 MHz in CDCl3) for selected compounds are given
below. Compound 5a: 8.15 (dd, 1H), 8.0 (d, 1H), 7.92 (d, 1H), 7.83 (dd, 1H), 7.36
(m, 4H), 6.76 (d, 1H), 4.10 (q, 2H), 1.24 (t, 3H). Compound 6b: 7.69 (dd, 1H), 7.64
(d, 1H), 7.30–7.12 (m, 5H), 7.0 (s, 1H), 6.94 (d, 1H), 6.88 (d, 1H), 6.85 (d, 1H),
6.42 (dd, 2H), 3.84 (s, 3H), 3.78 (s, 3H). Compound 6c: 7.80 (m, 2H), 7.40 (d, 1H),
7.33 (m, 2H), 7.24–7.15 (m, 2H), 7.10 (m, 1H), 7.0 (d, 1H), 6.80 (d, 1H), 6.54 (br
s, 1H), 6.43 (dd, 1H), 6.34 (d, 1H), 3.71 (s, 3H). Compound 6d: 7.69 (m, 2H), 7.38
(d, 1H), 7.21 (m, 2H), 7.13 (m, 2H), 6.88 (m, 1H), 6.83 (dd, 2H), 6.30 (dd, 1H),
6.26 (d, 1H). Compound 7b: 7.91 (d, 1H), 7.77 (d, 2H), 7.42 (dd, 1H), 7.36–7.27
(m, 3H), 7.20 (d, 1H), 7.12 (dd, 1H), 6.97 (dd, 2H), 6.81 (d, 1H), 6.75 (d, 1H).
Compound 8a: 7.94 (m, 2H), 7.15 (t ꢁ d, 1H), 7.08 (d, 1H), 6.87 (t, 2H), 6.64 (d,
1H). Compound 8c: 8.18 (d, 1H), 8.06 (dd, 1H), 7.24 (m, 2H), 6.94 (m, 3H).
Compound 9a: 7.89 (s, 1H), 7.40 (s, 2H), 7.22 (t, 2H), 6.95 (m, 6H), 6.80 (dd, 1H).
Compound 10a: 7.58 (d, 2H), 7.24 (m, 2H), 7.20 (d, 1H), 7.03 (dd, 1H), 6.96 (m,
3H), 6.77 (d, 1H), 6.68 (d, 1H). Compound 10c: 7.92 (m, 1H), 7.43 (m, 2H), 7.28
(m, 1H), 7.0–6.96 (m, 6H), 6.90 (d, 1H), 6.72 (d, 1H). Compound 11. 8.0 (m, 2H),
6.80 (d, 1H), 6.72 (d, 1H), 6.42 (d, 1H), 5.93 (d, 2H), 3. 72 (s, 3H). Compound 12a:
7.97 (dd, 1H), 7.53 (t, 2H), 7.21 (m, 3H), 6.84 (d, 1H), 6.52 (d, 1H), 5.90 (dd, 2H),
3.68 (s, 3H). Compound 13: 7.92 (s, 1H), 7.41 (s, 2H), 6.98 (m, 3H), 6.86 (d, 1H),
6.72 (d, 1H), 6.44 (d, 1H), 3.59 (s, 3H). Compound 16: 8.32 (d, 1H), 8.08 (d, 1H),
7.00 (d, 1H), 6.68 (d, 1H), 6.40 (d, 1H), 5.89 (s, 2H). Compound 17: 7.89 (dd, 1H),
7.36 (m, 2H), 7.16 (d, 1H), 7.0 (dd, 1H), 6.82 (d, 1H), 6.63 (d, 1H), 6.38 (d, 1H),
5.82 (s, 2H). Compound 19a: 7.49 (dd, 2H), 7.28 (m, 1H), 7.19 (m, 3H), 6.98 (d,
1H), 6.48 (d, 1H), 6.22 (d, 1H), 5.62 (dd, 2H). Compound 21a: 7.86 (t, 1H), 7.25
(m, 3H), 7.18 (d ꢁ t, 1H), 7.12 (t, 1H), 6.93 (d ꢁ q, 1H), 6.45 (d, 1H), 6.19 (d, 1H),
5.70 (s, 2H). Compound 22: 6.93 (t, 1H), 6.73 (d, 1H), 6.66 (m, 2H), 5.90 (d, 1H),
4.98 (s, 2H), 3.30 (s, 3H). Compound 23a: 7.62 (d, 2H), 7.16 (d, 2H), 7.12 (m, 2H),
7.0 (m, 2H), 6.66 (d, 1H), 6.36 (d, 1H), 5.85 (s, 2H). Compound 23c: 8.21 (d, 1H),
7.80 (dd, 1H), 7.61 (d, 1H), 7.10 (m, 3H), 6.67 (d, 1H), 6.34 (d, 1H), 5.88 (s, 2H).
All the synthetic products showed satisfactory analytical (13C NMR, MS) data,
consistent with the assigned structure.
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23. Synthesis of
2 (typical procedures): 2-Bromo-4-nitroanisole (4b) (425 mg,
1.8 mmol), 2-ethoxynaphthalen-1-ylboronic acid (800 mg, 2 equiv), Pd(PPh3)4
(100 mg, 5 mol%), and K2CO3 (735 mg, 3 equiv) were charged into a microwave
reaction vessel. To this vessel, a three-solvent mixture (5 ml) (DME/EtOH/H2O,
3:2:1) was added, and then the reaction mixture was irradiated in Biotage-
microwave initiator for 15 min. Reaction mixture was partitioned between
ethyl acetate and water. The organics were separated and washed with water,
brine, dried over Na2SO4, and concentrated (usual work up). The crude mass
obtained was purified by chromatography over silica gel, eluting with 5–8%
ethyl acetate in hexanes to provide 2-ethoxy-1-(2-methoxy-5-nitrophenyl)
naphthalene (5b) (580 mg, 98%). 1H NMR (400 MHz, CDCl3): d 8.35 (dd, 1H),
8.21 (d, 1H), 7.91 (d, 1H), 7.84 (m, 1H), 7.36 (m, 4H), 7.08 (d, 1H), 4.12 (q, 2H),
3.77 (s, 3H), 1.24 (t, 3H). 13C NMR (100 MHz): d 163.2, 153.9, 141.5, 133.3,
130.2, 129.2, 128.7, 128.4, 126.9, 126.7, 125.5, 124.6, 123.9, 119.9, 115.1, 110.7,
65.3, 56.4, 15.2. HRMS Calcd for C19H18N4O, 324.12263; observed 324.12303
(M+H). To a solution of 5b (525 mg, 1.62 mmol) in dichloromethane (15 ml),
BBr3 (3 equiv) was added at ꢀ78 °C and the reaction mixture was brought to
room temperature overnight. Reaction mixture was quenched by addition to
ice-cold water, and the product was extracted with ethyl acetate. The organic
28. Du, Y.; Rodina, A.; Aguirre, J.; Felts, S.; Dingledine, R.; Fu, H.; Chiosis, G. J.
Biomol. Screen. 2007, 12, 915.
29. QikProp, version 3.0, Schrodinger, LLC, New York, NY, 2005.
30. The SKBr3 breast cancer cells were grown in RPMI-1640 medium
supplemented with 10% FBS. 1250 cells in 50 ll of culture medium were
plated in 384-well microtiter plates (Costar) and allowed to attach for
overnight. After treated with either compounds or vehicle (DMSO) for 72 h,
the viability of the cells was measured by CellTiter-Blue (Promega). Briefly,

T. Ganesh et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4982–4987
4987
10
l
l
of CellTiter-Blue was added and incubated at 37 °C for 4 h. The
nonlinear regression analysis as implemented in Prism 4.0 (Graphpad
fluorescence intensity (FI) was measured using the Analyst HT plate reader
(Molecular Devices) with an excitation at 545 nm and an emission at 595 nm.
The IC50 was calculated as the compound concentration that inhibits cell
viability by 50% compared to vehicle control wells. The data reported are
average values from four replicates. IC50 values were determined using a
Software). O’Brien, J. et al. Eur. J. Biochem. 2000, 267, 5421.
31.
A
known pyrazole derivative was resynthesized as reported in Ref. 11a
(compound 16a from Ref. 11a) and used as a positive control in the biological
testing. This analog has shown IC50 value 1.6, 3.1 M in FP and cell growth
inhibition (against SKBr3 cells) assays, respectively.
l